Re-enable Cython support for Stackless Python
Re-enable Cython support for Stackless Python

Cython speedups were disabled in April 2017 (commit 5ea0f3b1), because of
Cython bugs that were fixed in August 2018
(https://github.com/cython/cython/pull/2554 and
https://github.com/cython/cython/pull/2556). And all Stackless versions
released after August 2018 contain a workaround for this bug. Therefore it is
now time to re-enable Cython speedups for Stackless Python.

fabioz/PyDev.Debugger,fabioz/PyDev.Debugger,fabioz/PyDev.Debugger,fabioz/PyDev.Debugger,fabioz/PyDev.Debugger